IPM - Debunking Myths

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Myth: The City treats the river for mosquitoes

Edmonton’s thirty five or so species of mosquitoes develop in standing water sites where, except for one species (Coquilletidia perturbans), all larval and pupal stages must breathe air using the undisturbed surface tension of the water. These stages cannot survive in flowing water or even choppy open water on a lake. Flowing water habitats are more suitable for other biting flies such as black flies.

The reason that adult mosquitoes are relatively common in Edmonton’s river valley system is that these are harbourage areas for adult mosquitoes which cannot generally tolerate drier conditions in the less treed uplands. Summer flowers in the valley also provide a succession of nectar sources that sustain the mosquito’s energy requirements.

Myth: Bats and purple martins control mosquitoes

Like most predators, these insectivores are opportunists feeding on a wide variety of flying insects, but searching for the most energy efficient food catch they can find. Locally, little brown bat scats do show remains of mosquitoes, but this is usually insignificant compared to moths, mayflies and various midges that swarm over larger bodies of water. Purple martins also like to catch larger prey such as dragonflies.

Well designed bat and purple martin boxes may not reduce mosquitoes compared to other flying insects in your yard, but they are certainly encouraged for wildlife conservation.

Myth: City mosquito spraying kills off mosquito predators like dragonflies

The City’s mosquito control program only targets larval stages of floodwater mosquitoes that develop in standing water habitats after snowmelt or a summer storm has raised the water level to flood and hatch their eggs. This egg hatching requirement confines them to temporary and semi-permanent standing water habitats. These habitats dry up in the fall, precluding organisms like dragonflies, that require more than a full year of development in the aquatic stage.

Biodiversity in these short-lived aquatic habitats is very low, leading to the potential for escalating outbreaks of nuisance mosquitoes, peaks of which were experienced in 1974, and 1983. Whereas drought conditions since 2002 have seen unprecedented low mosquito populations in Edmonton, dragonflies have been able to maintain a greater presence through their dependence on more permanent water habitats. Edmonton's mosquito management program encourages dragonfly development by avoiding control in more permanent water bodies.